Misfire under load

[this old xs]

I can't count how many times I've had those carbs on and off this thing My pro tip is choke on, then about 1/2 way through you need to go full throttle. I've got it down to a fine art, sadly.

Anyway, after last time I decided to err on the side of caution and just put the bare minimum amount of things on. I cranked the ever loving heck out of it with no plugs in. Should have got oil to all the right places.

Not going to lie, I was quite nervous starting it up. Man is this thing quiet! Like really quiet. Maybe that crank has been on the way out the whole time I've owned it, I dunno. Either way, I'm pretty happy I replaced the gearbox bearings too.

I took a video but can't upload it here and I only watch YouTube, not contribute, so you'll have to take my word for it.

She is purring like a kitten. This afternoon I'll put the rest back together and go for a spin. It would be too ironic if the misfire was still there.

 

[this old xs]

Aaaand it doesn't upshift past 2nd properly At first it wouldn't pass 2nd at all, but I fiddled with the clutch cable adjustment and did a couple of clutch less shifts and got more gears.

Believe me when I say I tested this at various stages of assembly! 1st to 2nd shift is completely normal, after that 50/50 if you get a normal shift or none at all. Really hope I don't have to split the cases again!

 

[this old xs]

Ok, so if I upshift half a dozen times I can get 4th and 5th. So I'm thinking maybe the ratchet on the shift lever or maybe I damaged the wheel or pins (not what they're called) on the shift drum.

Oh, and guess who's still got a full throttle under load misfire?

 

[this old xs]

Sticking point is 3rd to 4th shift. Everything else is normal. Having said that, it just shifted normally on the centre stand in the shed...

I noticed the gear change shaft is too far in when fitting the lever (I definitely put the e clip on) but I was too excited to go for a ride. Definitely warrants investigation.

 

[this old xs]

Might need to check this adjustment. I'm going for another ride to see if it magically fixed itself

 

[this old xs]

It didn't magically fix itself surprisingly. I had the bike leaned over on this jankety setup because I didn't want to change the oil again, but after I took the clutch cover off I could see a wee bit of gold glitter (which I'm guessing was the old conrod) so I dumped it. I'm choosing to believe that came from the cylinders and rocker housing which I stupidly forgot to clean the oil passages of.

Anyway, it makes no sense to me, because the bike was shifting well (for XS650 values of well) before, but see the adjustment for yourselves.

Before:

After:

I went for a little ride up and down. Twice it didn't shift 3rd to 4th, which is a significant improvement from pretty much always. I'm calling it good for now, though I'm certain I've done something wrong somewhere in there.

I'll address the misfire later. I did bend the advance weights to get enough adjustment on the points. I'm right at one end now, I can't remember if it's the opposite way to how it was or not, but I'll tweak the weights so I'm in the middle of the adjustment and see how that goes.

 

[this old xs]

Just went for a two up cruise with the boss, so good. 1 failed 3rd to 4th shift which is 100% more than before I pulled it apart but I think it'll come good. I tried to keep everything in the same place but I probably mixed up the shift drum followers in the shift forks. Might be bedding in in its new place.

The shifting would be described as "notchy" by one of those motorcycle writer types, but I think it was like that before. I've got a mate who rides a Moto Guzzi V65 and it's probably buttery smooth by comparison. Let's just say it rewards a confident shift.

I've owned a lot of bikes over the years, but I love riding this one the most of all. I must do, I've dumped thousands into it, though you wouldn't know by looking at it! Am I overcapitalised? Absolutely, but on a smiles for miles scale I'm way in front.

I'll tweak the advance weights back and dial in the timing (just set it statically) later and give a hopefully final update.

 

[Jim]

I'll tweak the advance weights back and dial in the timing (just set it statically) later and give a hopefully final update

If you're referring to the weight "stops" bent into the advance plate, I wouldn't bend 'em, they'll crack pretty easy.
Iirc, the factory put out a service bulletin saying to bend the taps to correct for too much advance. Then put out another after saying not to because they'll get brittle and break off. More than one of those plates have grenaded after being bent.

 

[Jan_P]

How about the clutch adjustment is that Perfect ?
Having it on the central stand and engine running ( Carefully ) shifting and operating the Clutch
I pull in the clutch and try to stop the wheel with the foot solid footwear.against the tire side.
If not good adjust .. if to loose it will slip

 

[Miker Vee]

Did you, at any point, disassemble the shift forks?
The cotter pins on those should be replaced in a specific position.
If positioned wrong, they may interfere with some other parts during the shifting.

 

[this old xs]

Did disassemble the shift forks (against my better judgement), don't recall how exactly I put the cotter pins in, but I think they're OK. If I shift firmly it never fails. Only missing, on average one 3rd to 4th shift per ride max. You can just retry and it goes immediately. Pretty sure I must have mucked up a follower and it needs to bed in.

I just replaced the advance rod bushings. I ordered them ages ago, but frankly I didn't want to do the work. A couple of days ago I noticed the advance rod had what I would consider a lot of slop. Time to suck it up.

As usual this forum comes through* and someone mentioned they used a 12mm anchor bolt. To get mine to fit I had to widen the slots so the sleeve would close up enough to fit in. I eventually worked out that I needed some grooves in it to grip, then it worked like a charm.

I set the points a couple of days ago and had to adjust to gap quite a bit after fitting the new bushings. Timing is pretty much spot on, advance goes to full advance. Too lazy to test, will hopefully get out for a cruise tomorrow.

Side note, my previous fuel consumption was around 6.4-6.5l/100km (36mpg). I measured it yesterday and it came in at 4.6l/100km (51mpg). Holy frictional losses batman! Thinking that crank was shagged from the get go.


*I would already have kicked some cash in the can, but for a deep and abiding hatred of PayPal.

 

[this old xs]

Update; 3rd to 4th shifting is getting better. Went for a ride today and no shifting problems, fuel consumption 4.7l/100km (50mpg).

Engine is so quiet, twice I mistook drive chain noise for engine destruction. Gave me quite the scare.

Today I did a job I've been putting off for ages but wanting to do since I got the bike. I took a screwdriver to the paint job on my fuel tank. A previous owner debadged the tank but I could just see the outline of the bracket and one screw hole.



I bottomed out the tap too hard in one hole and lifted the paint, but it's barely outside the badge. Looks so good!

 

[this old xs]

I keep forgetting to mention, Geoff called me about the crank. He forgot he gave me a price, things have gone up but he very kindly gave me a $100 store credit. I think I'll get a new advance unit because it still misfires under full throttle load at 4.5krpm. The low rpm misfire is completely cleaned up though.

Decided to check the low speed mixture and carb synchronisation. Also, I did the umpteenth oil change in a very short period the other day and I wasn't happy with the amount of glitter in the oil. I cleaned out the sump strainer but forgot about the side one. Took it out and it had a lot of debris in it.

I decided to follow in the footsteps of TooManyXS1Bs and 5twins and make a paper sleeve for the side cover strainer to try and filter out the fine particulate. I won't rehash it here, 5twins has covered the process in detail plenty of times, but I will say if you're in Australia it's an oil filter for the old 4 litre straight six Jeep. Any decent spare parts guy will find it OK but here's the numbers:



Unfortunately it'll cost a bit more than the $3 wall wallmart filter 5twins got!

My mate bought this fancy synchro king thingy which is not cheap but works so great. Carbs were still in perfect synch:



This is my janky o2 sensor/afr setup, but no way I'm butchering my headers!



I have ridden with this but it's not advisable. Left carb was a little rich on the low speed:



But easy fixed:



I can't recommend this enough. Eventually I'll rig it up so I can do some proper road testing.

 

[Dunc]

I keep forgetting to mention, Geoff called me about the crank. He forgot he gave me a price, things have gone up but he very kindly gave me a $100 store credit. I think I'll get a new advance unit because it still misfires under full throttle load at 4.5krpm. The low rpm misfire is completely cleaned up though.

Decided to check the low speed mixture and carb synchronisation. Also, I did the umpteenth oil change in a very short period the other day and I wasn't happy with the amount of glitter in the oil. I cleaned out the sump strainer but forgot about the side one. Took it out and it had a lot of debris in it.

I decided to follow in the footsteps of TooManyXS1Bs and 5twins and make a paper sleeve for the side cover strainer to try and filter out the fine particulate. I won't rehash it here, 5twins has covered the process in detail plenty of times, but I will say if you're in Australia it's an oil filter for the old 4 litre straight six Jeep. Any decent spare parts guy will find it OK but here's the numbers:

View attachment 342124

Unfortunately it'll cost a bit more than the $3 wall wallmart filter 5twins got!

My mate bought this fancy synchro king thingy which is not cheap but works so great. Carbs were still in perfect synch:

View attachment 342125

This is my janky o2 sensor/afr setup, but no way I'm butchering my headers!

View attachment 342126

I have ridden with this but it's not advisable. Left carb was a little rich on the low speed:

View attachment 342127

But easy fixed:

View attachment 342128

I can't recommend this enough. Eventually I'll rig it up so I can do some proper road testing.

I keep forgetting to mention, Geoff called me about the crank. He forgot he gave me a price, things have gone up but he very kindly gave me a $100 store credit. I think I'll get a new advance unit because it still misfires under full throttle load at 4.5krpm. The low rpm misfire is completely cleaned up though.

Decided to check the low speed mixture and carb synchronisation. Also, I did the umpteenth oil change in a very short period the other day and I wasn't happy with the amount of glitter in the oil. I cleaned out the sump strainer but forgot about the side one. Took it out and it had a lot of debris in it.

I decided to follow in the footsteps of TooManyXS1Bs and 5twins and make a paper sleeve for the side cover strainer to try and filter out the fine particulate. I won't rehash it here, 5twins has covered the process in detail plenty of times, but I will say if you're in Australia it's an oil filter for the old 4 litre straight six Jeep. Any decent spare parts guy will find it OK but here's the numbers:

View attachment 342124

Unfortunately it'll cost a bit more than the $3 wall wallmart filter 5twins got!

My mate bought this fancy synchro king thingy which is not cheap but works so great. Carbs were still in perfect synch:

View attachment 342125

This is my janky o2 sensor/afr setup, but no way I'm butchering my headers!

View attachment 342126

I have ridden with this but it's not advisable. Left carb was a little rich on the low speed:

View attachment 342127

But easy fixed:

View attachment 342128

I can't recommend this enough. Eventually I'll rig it up so I can do some proper road testing.

I'd run it around 12-12.5 AFR as that produces the best power & wont hurt it in the heat. 14 would be OK at idle but too lean under load/acceleration.

 

[this old xs]

Good to hear. It goes about 12 when I rev it but that's no load obviously. I did a little ride with it hooked up once and IIRC it was hitting 9 at full throttle acceleration.

 

[this old xs]

Welp, I haven't pulled it down yet, but the money pit has done the right hand bigend again. Once you know the sound, you know the sound. Also, endless forbidden glitter in the several oil changes I've done in the only 500 or so miles I've ridden since reassembly.

On the plus side, the paper oil filter sleeves work well:



I 100% cleaned the cases very thoroughly, but, incredibly I forgot about the cylinders and head. I guess it's possible there was enough contamination there to cause this? Manufacturing defect seems improbable? One rod was a different colour to the other one which I thought was a bit weird.

Regarding the subject of this thread, a while back I got caught in heavy rain and the misfire got worse, as in occurring at a smaller throttle opening. I reckoned it must be the main connector, the 6 pin from the alternator to the wiring harness. I cleaned the sockets and its back where it was in terms of throttle position, but still there.

I also whacked my 137.5 mainjets in just to see, but if anything it felt worse, misfiring at smaller throttle openings. Bit of a secondary problem at the moment I guess. Sigh.

I see 2nd hand cranks on ebay in the USA...

 

[Its been a long time]

Oh dear. How long did it run before the right side big end sounded bad again? Edited to say - Ah, just 500 miles. Most likely explanation in my experience of machines with ball or roller bearing bottom ends would suggest the presence of failure debris caused the second failure.

 

[this old xs]

500 or so miles

 

[Its been a long time]

500 or so miles

Apologies, I amended my post.

 

[5twins]

ANY main jet increase over stock in the '78-'79 carb set requires you to lean the needles a step or the upper midrange will be too rich. That will give you break-up and stumbling under heavy throttle through that RPM range (say about 4 to 5K).